AN EXPANDED WEIGHTED-AVERAGING MODEL FOR INFERRING PAST TOTAL PHOSPHORUS CONCENTRATIONS FROM DIATOM ASSEMBLAGES IN EUTROPHIC BRITISH-COLUMBIA (CANADA) LAKES

Eighteen lakes were added to a published training set of 46 British Co lumbia (BC) lakes in order to expand the original range of total phosp horus (TP) concentrations. Canonical correspondence analysis (CCA) was used to analyze the relationship between diatom assemblages and envir onmental variables. Specific conductivity and [TP] each explained sign ificant (P less than or equal to 0.05) directions of variance in the d istribution of the diatoms. The relationship between diatom assemblage s and [TP] was sufficiently strong to warrant the development of a wei ghted-averaging (WA) regression and calibration model that can be used to infer past trophic status from fossil diatom assemblages. The rela tionship between observed and inferred [TP] was not improved by the ad dition of more eutrophic lakes, however the [TP] range and the number of taxa used in the transfer function are now superior to the original model. Diatom species assemblages changed very little in lakes with T P concentrations greater than 85 mu g l(-1), so we document the develo pment of a model containing lakes with TP less than or equal to 85 mu g l(-1). The updated model uses 59 training lakes and covers a range o f species optima from 6 to 41.9 mu g l(-1) TP, and a total of 150 diat om taxa. The updated inference model provided a more realistic reconst ruction of the anthropogenic history of a highly eutrophic BC lake. Th e model can now be used to infer past nutrient conditions in other BC lakes in order to assess changes in trophic status.